1. Field of the Invention
The present invention is concerned with a portable timepiece, such as a wrist or pocket watch, and more particularly relates to a timepiece having a rotatable bezel.
2. Description of the Related Art
It has hitherto been the case that a bezel mounted on a case band rotatably is held in a desired operating position by a structure producing a click feeling with its rotation. A click ball type and a leaf spring type are known as the structure for that purpose.
The click ball type has a click groove formed in the rear surface of a bezel and having engaging teeth formed by a plurality of serrations lying in the direction of rotation of the bezel, a steel ball engageable with the engaging teeth and a coil spring holding the steel ball against the engaging teeth. According to this structure, the rotation of the bezel in either of clockwise and counterclockwise directions as desired causes the steel ball to be pressed by the engaging teeth and deform the coil spring, whereby the rotation of the bezel is allowed. Each rotation of the bezel by a certain angle causes the steel ball to fall between every two adjoining engaging teeth of the click groove owing to the force of the coil spring and thereby produce a click feeling. Moreover, the steel ball falling between the engaging teeth of the click groove in the rotational position of the bezel in which its rotational force has been lost holds the bezel in its rotational position as desired (reference is made to, for example, Japanese Patent Publication JP-A-2003-270365 (Paragraphs 0002-0009 and FIG. 3)).
The leaf spring type has gear-like teeth formed on the case band of a watch case and a locking member and a pressing member which are attached to a bezel mounted rotatably on the case band. The locking member has a first locking portion which is engageable with the teeth on the case band for prohibiting the rotation of the bezel in one direction, and a second locking portion engageable with the teeth for prohibiting the rotation of the bezel in the direction opposite the one direction. The first and second locking portions are each formed by a leaf spring. The pressing member is a push button for pressing the first locking portion away from the teeth. Therefore, the bezel is rotatable in the one direction when the pressing member is pushed (while the second locking portion is elastically deformed to allow the passage of the teeth), and when the pressing member is released from pressure in any desired rotational position of the bezel, the first locking portion engages the teeth owing to its own elastic force. As a result, both of the first and second locking portions engage the teeth on the case band to ensure that the bezel be held in its desired rotational position (reference is made to, for example, Japanese Patent Publication JP-A-2005-326280 (Paragraphs 0015-0038 and FIGS. 1-10)).
Although the prior art on the click ball type makes the bezel rotatable in either of the clockwise and counterclockwise directions, it is only with low reliability that the bezel can be held in its desired rotational position, since only the force of a coil spring is relied on for holding the bezel in its desired rotational position. Therefore, it is possible that the bezel may be inadvertently rotated by an external force acting on the bezel when the time piece is carried.
As the prior art on the leaf spring type restricts the rotation of the bezel to one direction, it is impossible to reverse the rotation of the bezel in the event that an erroneous operation has caused the bezel to rotate somewhat away from its desired rotational position. Therefore, it is necessary and troublesome to give the bezel a substantially full rotation to bring it into its desired rotational position. Moreover, as the rotation of the bezel by pushing the pressing member attached thereto causes the movement of not only the bezel, but also the user's finger pushing the pressing member, an operational inconvenience arises from a tight and uncomfortable motion of the operating hand, particularly at the joint of the wrist, when a large amount of rotation has to be made, as when a substantially full rotation is given to the bezel with the timepiece worn on the wrist.